The present invention relates generally to a reciprocating piston compressor assembly and, more particularly, to improvements in a valve system for such a compressor assembly having suction valving associated with the piston assembly and discharge valving associated with a valve plate closing the compression cylinder.
In a typical reciprocating piston compressor, a cylinder is defined by a compressor crankcase and a piston reciprocates within the cylinder to compress gaseous refrigerant therein. In a compressor to which the present invention pertains, the piston comprises a piston valve assembly wherein a suction valve is operably mounted to the piston head to receive gas through the piston from one end of the cylinder and compress the gas in the cylinder for discharge out the other end thereof. A valve plate is mounted to the crankcase so as to close the top of the cylinder. The valve plate includes a discharge valve assembly operable to discharge gas into a discharge space defined by a cylinder head cover mounted to the crankcase with the valve plate disposed therebetween.
A scotch yoke compressor includes a suction cavity defined within the crankcase into which a plurality of radially disposed cylinders open. A crankshaft is journalled in the crankcase and includes an eccentric portion located in the suction cavity to which the pistons and cylinders are operably coupled by means of a scotch yoke mechanism. In a typical scotch yoke coupling mechanism, where four radially disposed pistons are attached to a pair of U-shaped yokes, the piston bodies are attached to the yokes by means of threaded bolts, rivets, and the like. In addition, separate means are provided for retaining the suction valve components to the piston head. Such valve attachment means generally comprise bolts, rivets, bosses, and the like. The provision of separate means for attaching the piston member to the scotch yoke and for attaching suction valving to the piston head requires a plurality of parts and entails a higher degree of difficulty during compressor assembly.
In a compressor assembly having a piston valve assembly, as herein described, the suction valve retaining member generally includes a protruding portion such as a buttonhead which extends from the piston head toward the radially outward end of the cylinder. In order to reduce the amount of reexpansion volume remaining in the cylinder when the piston is at top dead center, it is desirable to have the piston travel as close to the valve plate covering the cylinder as is possible. To this end, any protrusion above the piston head top surface is preferably received within a recess in the valve plate.
Accordingly, the prior art devices having piston valve assemblies have provided for recesses mill cut into the valve plates covering the cylinders. However, these prior art devices require thicker valve plates and milling during manufacture of the valve plate to provide an adequate recess. With the requisite thicker valve plate, discharge ports extending through the valve plate are made longer, thereby increasing reexpansion volume associated therewith. Efforts to recess the discharge valve slightly into the top face of the valve plate have addressed these discharge port reexpansion problems, however, additional machining of the valve plate is required and the initial thickness of the valve plate must remain sufficient to provide the recess required by the piston valve assembly protrusion.
While the provision of a piston valve assembly in the aforementioned scotch yoke compressor provides additional room and flexibility for placement of a discharge valve assembly on the top surface of the valve plate, prior art discharge valve assembly designs have not taken full advantage of the additional space and flexibility. For instance, a typical discharge valve assembly includes an annular valve element for covering circularly arranged discharge ports in the valve plate. Heretofore, the space radially inwardly from the annular valve element has been used to provide a central guide on which the valve element rides to provide a retaining member to limit valve lift. In such an arrangement, the inside diameter is blocked and, accordingly, all discharge of gas is to the outside diameter of the discharge valve, thereby requiring greater valve lift which results in detrimental valving impact and noise.